Hydrostatic multi-motor drive

ABSTRACT

With a hydrostatic multi-motor drive unit with a least two hydraulic motors acting upon a common load, a solution should be created, with which a further operating range is covered by the use of several motors and at the same time a simple as possible and problem free coupling of the motors is assured. Furthermore, a method for controlling the drive unit is indicated, which permits continuous transitions between the different operating ranges. This is achieved in that the motors ( 2, 3 ) are connected with each other through at least one freewheel device ( 4 ), in which the motor ( 2 ) arranged after the freewheel device has a variable displacement volume.

BACKGROUND OF THE INVENTION

The present invention relates to hydrostatic multi-motor drive unitsand, more particularly, to such a unit with at least two hydraulicmotors acting upon a common load.

Hydraulic drives with two motors are known in essentially two differentversions or designs.

In a first design both drives are rigidly interconnected by a shaft and,hence, both run permanently. In arrangements in which at least one ofthe motors is designed to be adjustable, and for attaining high speeds,this motor is set to zero by adjusting its displacement volume to zero.It is disadvantageous that the motor which is set to zero is draggedalong by the other motor and, as a result of this, high mechanicallosses occur.

To avoid such problems, two-motor drive designs are known in which thetwo motors are interconnected by gears and couplings, so that in theoperating ranges in which the adjustable motor is set to zero, thismotor can be mechanically disconnected from the second motor. Thedisadvantage of this solution is in the high complexity of the couplingand arrangement of gears which is necessary in order to guaranteesynchronization of the two machines when engaging and disengaging, sothat a smooth transition between the various different operating rangesis made possible.

In DE 100 60 679 A1 an additional hydrostatic two-motor drive unit isdisclosed in which two motors are connected with at least one coupling.Such a drive unit encounters the above-described disadvantages.

It would be a great advantage to provide a hydrostatic multi-motor driveunit that overcomes the above problems and disadvantages.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide animproved multi-motor drive unit that avoids the above-noteddisadvantages.

It is another object of the present invention to provide a multi-motordrive unit which covers a wide operating range through the use ofseveral motors and at the same time guarantees coupling of the motors.

It is a further object of the present invention to provide a multi-motordrive unit that is as simple as possible and free from problems.

It is a further object of the present invention to provide a multi-motordrive unit that interconnects the motors through at least one freewheeldevice, such that the motor arranged behind the freewheel device has avariable displacement volume.

It is a still further object of the present invention to provide amethod for controlling a multi-motor drive unit which permits continualtransitions between the various operating ranges.

These and other objects are achieved by providing method and apparatusfor controlling a hydrostatic multi-motor drive unit which permitscontinuous transitions between the different operating ranges. This isachieved by interconnecting the motors through at least one freewheeldevice, in which the motor arranged after the freewheel device has avariable displacement volume.

BRIEF DESCRIPTION OF THE DRAWINGS

The advantages of this invention will be apparent upon consideration ofthe following detailed disclosure of the invention, especially whentaken in conjunction with the accompanying drawings wherein:

FIG. 1 is a diagrammatic overview of a multi-motor drive unit inaccordance with the invention with an adjustable motor;

FIG. 2 is a cross section through a freewheel device depicted as anexample for the solution of the multi-motor arrangement in accordancewith the invention;

FIG. 3 is a diagrammatic overview of the multi-motor drive unit with twoadjustable motors;

FIG. 4 is a depiction of the multi-motor drive with a switchablecoupling;

FIG. 5 is a depiction of the hydraulic circuit for a multi-motor driveunit in accordance with the invention; and

FIG. 6 is a depiction of the driving characteristics of the multi-motordrive.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIG. 1, a multi-motor drive unit in accordance with theinvention, generally designated by 1, comprises a hydraulic motor 2which is variable in its displacement volume and a hydraulic motor 3with a constant displacement volume. These are interconnected via amechanical freewheel device 4. A variable displacement hydraulic pump 5provides the hydraulic circuit with pressure medium via pipes 6 and 7.

At least one pressure sensor with a measurement signal transformer 8measures the pressure in the hydraulic circuit and passes it on in theform of an electrical signal to a control unit 9. This calculates fromthe measured parameters of status in the circuit and the desired valuesprescribed by the user, the correcting signals, and with these adjuststhe volume of the variable motor 2 through the motor controller 9 b andwith the pump controller 9 a adjusts the displacement volume of thevariable displacement pump 5.

Thus, depending upon the volume flow of pump 5 and the motor volume ofthe adjustable motor 2, a rotational speed of the motors is set.Depending upon the setting of the adjustable motor 2, the volume flow ofpump 5 is divided between the two motors 2 and 3, in which, because ofthe parallel circuit of the motors, the same pressure difference isapplied to both motors and the freewheel device is locked and at thesame time the torque of both motors is transmitted to the driving axle,until the torque given out by the adjustable motor is zero and this is,then, at a standstill. Thus, both motors 2 and 3 together drive a load10, e.g. the running gear of a vehicle.

The freewheel device 4 consists, as depicted in FIG. 2, as an example ofan outer ring 11, which is connected non-positively with the motor onthe load side. In the center of the ring 11 there is a star-shaped wheel12, which is connected to the adjustable motor 2. If the star-shapedwheel 12 is driven, the metal balls 13 rolling on the outer surface ofthe crank become jammed against the inner surface of the ring 11 andthus effect a transmission of power from the star-shaped wheel 12 to theouter ring 11. If the outer ring 11 is moving faster than thestar-shaped wheel 12, the balls fall into recesses in the wheel 12 andthere is no transmission of motion from the outer ring 11 to thestar-shaped wheel, so that the ring 11 can turn freely in thisdirection.

An alternative possibility, in which both motors are variable, isdepicted in FIG. 3. Here, as well as the first variable motor 2, alsothe motor on the load side 3′ is variable and can be adjusted by thecontroller 9, depending on the current state of the drive unit and thedesired set parameters. Thus, it is possible to further increase theoperating range of the drive unit.

When traveling backwards no transmission of power through the freewheeldevice 4 from the motor 2 to the load 10 is possible. For the case whenoperating backwards the same maximum torque should be available at theload as in forwards operation, a controllable clutch 14 in parallel withthe freewheel device is envisaged, as depicted in FIG. 4. This is closedin reverse operation and thus makes possible transmission of power frommotor 2 via motor 3 to the load 10 also the freewheeling direction ofthe freewheel device 4.

The construction of the hydraulic circuit is shown in more detail inFIG. 5. An internal combustion engine 15 drives the variabledisplacement pump 5 and at the same time drives a fixed displacementpump 16, which preloads the low-pressure circuit 18, which consists inits essentials of a pressure medium reservoir 17 and a pressure controlvalve 19.

The low-pressure circuit 18 is connected with the high pressure circuitvia two non-return valves 20 and 21. These are protected againstdestruction by overpressure in the circuit by two pressure relief valves22 and 23. Connected to them via the pressure medium pipes 6 and 7 isthe driving part with the two hydraulic motors 2 and 3, which areinterconnected by the bypassable freewheel device 4 through thecontrollable clutch 14.

The power transmitted to the load 10 is determined by the variabledisplacement pump 5, which is driven at a particular rotational speed bythe internal combustion engine 15. The emitted volume flow of thepressure medium is determined by setting the displacement volume of pump5. The ratio of rotational speed and torque this power is transmitted tothe load 10 is determined by the setting the motor volume of thevariable motor 2.

The characteristic curve of the drive unit 1 in the forwards operationis depicted in FIG. 6 in principle. This shows a diagram in which thetorque is conveyed to the load through the rotational speed. Forstarting up the motor at point A, the displacement volume is increased,for which the motor volume of the variable motor is at a maximum. Byincreasing the pump volume flow, the rotational speed of the motorincreases up to the maximum or to a previously chosen set value of thepump displacement volume at point B. To further increase the rotationalspeed, the motor volume of the variable motor is reduced, which leads toreduction of the torque delivered to the load. The decrease in motorvolume requires that the available volume must flow through the motorvolume, which becomes smaller in total for both motors, as a result ofwhich the increase in rotational speed is affected. At point C thevolume of the variable motor 2 is reduced to zero, so that the entireavailable volume flow now flows only through motor 3. In the case thatonly motor 2 is variable and the pump is already set to maximumdisplacement volume, the maximum rotational speed is reached. If alsomotor 3′ is variable, this motor volume can likewise be reduced, whichbrings about a further increase in rotational speed. The maximumrotational speed is then attained at point D, at which the maximum pumpvolume flows through the minimum motor volume of the variable motor 3′and motor 2 because of its reduced volume of zero stands still, as aresult of which it is uncoupled from the load by the freewheel device 4.

The use of several motors offers the advantage that smaller motors canbe employed yet, nevertheless, in common operation a high torque isobtainable. In addition, however, through their small construction theyenable a high speed which is advantageous, for example, for the rapidtravel of mobile machine tools. Through the application of a freewheeldevice it is possible that all the motors can be run in the blockingdirection of the freewheel device for producing a high driving torque.In the ranges of rapid travel, then, the motors arranged behind thefreewheel devices with the displacement volumes set to zero, aredisconnected by the freewheel device of the motor arranged before thefreewheel device, which as a result is provided with the entire volumeflow of the pump(s) for attaining a high speed. Thus, with large motordisplacement volumes a high torque can be produced at low rotationalspeeds, and, conversely, increase the speed with a constant supply ofpressure medium, if the motor displacement volume is reduced. Onreduction of the motor displacement volume to zero, the motors arrangedafter the freewheel device stand still and then, as long as theirdisplacement volumes remain at zero, are no longer involved in providingdriving power.

Problems with synchronization do not occur, since as soon as thedisplacement volume of the motors arranged behind the freewheel deviceis increased again, their speed rises until the freewheel device isblocked and the torque produced by the previously disconnected motor istransmitted via the freewheel device to the driving axle, i.e. thetorque of all the motors is utilized additively to drive the load.

If a common pressure medium circuit is employed for all of the motors,an equilibrium of forces is established in the entire system and agentle start up and slowing down of the motor disconnected by thefreewheel device is achieved without additional control devices.

With the use of such motors, the advantages of the freewheel device canbe utilized particularly favorably, since in the low speed range withhigh torques the motors are mechanically coupled by the freewheeldevice. By reducing the motor volume the speed increases until thevolume of one of the motors is reduced to zero, so that only theremaining motor, now disconnected by the freewheel, serves for thedrive.

The pressure sensor in the pipe(s) between the pump and the motor candistinguish between the operating states of acceleration ordeceleration.

A preferred embodiment of the multi-motor drive unit is characterized inthat for supplying the motors with pressure medium an adjustable pump isenvisaged. The use of an adjustable pump has a series of advantages incomparison with the constant delivery pump with a control valve, i.e. asimple continuously controllable flow of pressure medium which can beutilized for controlling the drive unit. The controllable supply ofpressure medium in combination with the motor control offerspossibilities for varying the motor power over wide ranges andcontinuous transfer of power. Furthermore, through dispensing withcontrol valves in the power chain the drive system is very energyefficient because of avoidance of energy losses in the valvearrangements.

In a further embodiment of the invention it is envisaged that the motorsare connected in parallel to the freewheel device by a switchablecoupling. The parallel switchable coupling makes possible a powertransfer also in the direction of the freewheel device. This has theadvantage that in cases in which the drive should possess a comparableperformance characteristic both in the forwards and backwards direction,the freewheel device can be bypassed. Thus, also in both directions allof the motors present can be operated together and a correspondinglyhigh torque is available at the driving axle.

To solve the problem posed, the invention proposes also a process forinfluencing the power and/or the direction of rotation of the driveunit, which consists in that the displacement volume of the pump changesand/or the volume of a motor is adjusted and/or the volume of furthermotors is adjusted and/or the coupling is locked. To accelerate amulti-motor drive unit in the forwards direction, first the displacementvolume of the pump is increased, to further increase the speed thevolume of the motor arranged after the freewheel device is reduced andif necessary the volume of the further motors arranged after thefreewheel device is reduced.

Through increasing the displacement volume of the pump the flow ofpressure medium through the motors increases, which leads toacceleration of the drive unit. If the speed is to be further increased,the volume of a first motor is reduced, which with a constant flow ofpressure medium to this motor leads to an increase in speed withdecreasing driving torque. If several mechanically coupled motors aredepending upon the same pressure medium circuit the flow of pressuremedium is redistributed with a reduction in the volume of one motor, inwhich a greater part of the pressure medium flows to the motors withconstant volume, which overall leads to an increase in the speed of allthe motors. If the volume of one motor is reduced to zero, pressuremedium no longer flows through it, it no longer contributes drivingtorque and can also no longer be driven by the remaining motors arrangedahead of the freewheel device in the direction of freewheeling, so thatit remains disconnected by the freewheel device and stands still and theentire flow of pressure medium flows through the remaining motors.

The maximum rotational speed is reached if for maximum displacementvolume of the pump the volume of all the motors is reduced to theminimum value and in the extreme case all but one motor stands still andthe remaining motor disconnected by the freewheel device from thestationary motors runs at maximum speed because of the minimum totalflow of pressure medium, which differs from zero.

A further mode of operating according to the invention serves fordecelerating a multi-motor drive unit, and is characterized in that thepump works as a motor, all of the motors arranged ahead of the freewheeldevice are working as a pump with a displacement volume greater thanzero, and the volume of the further motors arranged after the freewheeldevice is set to zero.

With this procedure it is possible to achieve an especiallyenergy-saving deceleration of the drive unit. In doing so, the powertransmitted in motor operation of the pumps to their drive shaft can beutilized for driving further mechanical components, and need not beconverted into heat. In order to achieve this, the desired deceleratingbehavior of the drive unit must be achieved through appropriate controlmeasures at the adjustable pumps and motors. Such a condition occurs ifthe differential pressure applied through the motor(s) reverses its signand the kinetic energy of the load is given back to the hydrauliccircuit. By adjusting the displacement volume of the pump, and whenemploying a motor controllable by adjustment of the displacement volumeahead of the freewheel device, the deceleration of the drive unit (theload) and the amount of the energy given off to the other consumingunits coupled to the pump can be regulated.

A method in accordance with the invention for accelerating themulti-motor drive unit in a reverse direction consists in that thedelivery direction of the pump is reversed, the displacement volume ofthe pump is increased, and for the further increase in the speed whenemploying an adjustable motor ahead of the freewheel device itsdisplacement volume is reduced. This method serves for the simpleoperation of the multi-motor drive unit in the reverse direction.Through pumps capable of being adjusted to zero a reversal of thedelivery direction of the flow of pressure medium in the circuit ispermitted. As a result of this the motors likewise move in the reversedirection. By increasing the displacement volume of the pump andreduction of the displacement volume of the adjustable motor, as alreadydescribed above, the rotational speed of the drive unit and hence thedriven load can be increased.

In addition the invention concerns a process for accelerating themulti-motor drive unit in the reverse direction, which is characterizedin that the switchable coupling is closed, in order to bypass thefreewheel device in the freewheeling direction and the direction of thedelivery of the pump is reversed, the displacement volume of the pump isincreased, to further increase the rotational speed the volume of one ofthe first motors is reduced and if necessary the volume of the furthermotors is reduced.

So that such a multi-motor drive unit in slow operation possesses thesame driving characteristics in the forwards as in the backwardsdirection, as described above, a coupling can be employed in parallelwith the freewheel device. The coupling is then closed for operation inthe reverse direction and then the delivery direction of the pump isreversed, as a result of which all the motors are driven with a volumegreater than zero by the reverse oil flow in the backwards direction. Byincreasing the displacement volume of the pump, the rotational speed ofthe drive can be increased, as the oil flow is automatically dividedbetween the drives. To further increase the rotational speed, then,analogously, to the method in the forwards direction, the volume of themotors is reduced one after the other, until a maximum rotational speedof the entire arrangement is attained.

Naturally, the invention is not limited to the foregoing examples, butit can also be modified in many ways, without departing from the basicconcepts. In particular, the number of motors is not restricted to two,but it can perfectly well be more, as a result of which the flexibilityof the drive unit is further increased, as a distinctly greater speedrange or greater motor torque can be produced. Also, the combination ofvariable and non-variable motors is not limited to the above example.Furthermore, such a drive unit can be incorporated into generalhydraulic circuits, with which the many and diverse hydraulically movedloads present in a vehicle driven in such a manner could be operatedwith a comprehensive control concept.

1. A hydrostatic multi-motor drive unit comprising: at least twogearless, hydraulic motors acting upon a common load; a closed hydrauliccircuit containing said at least two hydraulic motors; at least onevariable displacement pump in said closed hydraulic circuit forsupplying the pressure medium to said at least two hydraulic motors;said at least two hydraulic motors interconnected by at least onefreewheel device, with one of said at least two hydraulic motorsarranged after said freewheel device; and said hydraulic motor arrangedafter said freewheel device having a variable displacement volume. 2.The drive unit of claim 1, further including: at least one pressuresensor in said hydraulic circuit between said at least two hydraulicmotors and said variable displacement pump for distinguishing betweenthe operating states of accelerating or decelerating.
 3. The drive unitof claim 2, further including: a controllable coupling interconnectingsaid at least two hydraulic motors in parallel with said freewheeldevice.
 4. The drive unit of claim 3, wherein: said at least twohydraulic motors, said freewheel device, and said controllable couplingare arranging in one casing.
 5. The drive unit of claim 4, furtherincluding: an electronic control unit connected to and managing thevariables of said at least two hydraulic motors and said variabledisplacement pump.
 6. The drive unit of claim 5, wherein: saidelectronic control unit comprises a microprocessor.
 7. The drive unit ofclaim 1, further including: a controllable coupling interconnecting saidat least two hydraulic motors in parallel with said freewheel device. 8.The drive unit of claim 7, wherein: said at least two hydraulic motors,said freewheel device, and said controllable coupling are arranging inone casing.
 9. The drive unit of claim 8, further including: anelectronic control unit connected to and managing the variables of saidat least two hydraulic motors and said variable displacement pump. 10.The drive unit of claim 9, wherein: said electronic control unitcomprises a microprocessor.
 11. The drive unit of claim 10, furtherincluding: a controllable coupling interconnecting said at least twohydraulic motors in parallel with said freewheel device.
 12. A methodfor influencing the power and the direction of rotation of thehydrostatic multi-motor drive unit of claim 3, comprising the steps of:(a) varying the displacement volume of said displacement pump; (b)varying the volume of one of said at least two hydraulic motors; (c)engaging or disengaging said controllable clutch to determine thedirection of rotation of said load.
 13. The method of claim 12, furthercomprising the steps of: (d) increasing the displacement volume of saiddisplacement pump; (e) for further increases in the rotational speed,the volume of said one of said at least two hydraulic motors is reducedand, if even additional rotational speed is desired, the volume of theother said one of said at least two hydraulic is reduced.
 14. The methodof claim 13, further comprising the steps of: (f) observe said pressuresensor, and when a pressure change in said hydraulic circuit isrecognized; (g) adjusting the displacement volume of said displacementpump.
 15. A procedure in accordance with claim 6 for accelerating amulti-motor drive unit in the reverse direction, characterized in that,the delivery direction of the pump (5) is reversed, the displacementvolume of the pump (5) is increased and to further increase therotational speed the volume of the motor (2) is reduced.